The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent the work is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Referring now to FIG. 1, an exemplary physical vapor deposition (PVD) system 10 is shown. For discussion purposes only, a hollow cathode magnetron (HCM) sputtering system is shown. The PVD system 10 includes a cathode 16 with a cathode target housing 18 and a cathode target 20. An anode 24 includes an anode ring 28, which is arranged adjacent to the cathode target 20. An adapter 34 is arranged adjacent to the anode 24 and includes an adapter ring 38. A pedestal 42 is arranged in a chamber 40. Both direct current (DC) and/or radio frequency (RF) biases may be applied to the pedestal 42. Electrostatic charge (ESC) may be used to releasably attach a substrate 44 such as a wafer to a cathode-facing surface of the pedestal 42.
In use, an inert gas is supplied in the chamber 40 near the cathode target 20. For example only, the inert gas may include Argon gas. A high voltage and vacuum is typically applied to the inert gas to ionize the gas, which creates plasma (hereinafter plasma ignition). Magnets and/or electromagnets 50, 52, 54, and/or 56 may be provided to shape and concentrate the plasma as will be described below. The magnets and/or electromagnets 50 may be rotatable.
A voltage supply V supplies a negative DC voltage across the cathode target 20 and the adapter ring 38. The adapter ring 38 and the chamber 40 may be connected to chassis ground or another reference potential. The anode ring 28 is allowed to float. In other words, the anode ring 28 is neither grounded nor biased.
In the example shown in FIG. 1, the cathode target 20 may have a cup-like shape to help concentrate the plasma. The cathode target 20 supplies metal material for sputtering. For example only, the cathode target 20 may be made of aluminum, tantalum, or other suitable metal that is to be deposited onto the substrate 44.
Magnetic fields may be produced by the magnets and/or electromagnets 50, 52, and/or 54. Additional magnets or electromagnets 56 may be arranged downstream of the cathode target 20 near the anode 24. The magnets or electromagnets produce a variable ion flux that may be used to control deposition, etch rate and/or uniformity.
For example, the magnets and/or electromagnets near the cathode target 20 trap free electrons in a magnetic field near a surface of the cathode target 20. The trapped electrons are not free to bombard the cathode target 20 to the same extent as with diode sputtering. A path travelled by these electrons when trapped in the magnetic field enhances their probability of ionizing a neutral gas molecule by several orders of magnitude. The increase in available ions significantly increases the rate at which target material is eroded and subsequently deposited onto the substrate 44.
The anode 24 and anode ring 28, which are typically held at plasma floating potential, may also be used in conjunction with the magnets and/or electromagnets to shape the plasma distribution. Ion energy and an etch rate can be controlled by applying an RF bias to the pedestal 42. An additional function of the pedestal 42 may include wafer temperature control during deposition and sputtering.
For some processes, relatively low chamber pressures and flow rates may be used. For example, some processes may use 2 standard cubic centimeters per minute (SCCM) flow Argon gas and chamber pressures of approximately 2×10−4 torr. When running at these low pressures and flow rates, it may be difficult to ignite the plasma, which may cause a time-out error during startup.
As a result, these low pressure processes tend to require significantly higher bias voltages to ignite the plasma as compared to higher pressure processes. Normally, the plasma may be ignited between the adaptor ring 38 and the cathode target 20, which may involve a relatively large gap.